328 Mr. W. C. Minor on Natural and Artificial Section 



further, that in Nais rivulosa, and, as far as I know, in Dero 

 limosa and in Enchytrceus triventralopectinatus, all of which have 

 short upper lips, the buds are given off at one point, though 

 that point may vary in different Naids of the same species, or 

 in one and the same Naid at different times. In the latter case, 

 the variation occurs as part of a peculiar form of fission of which 

 I shall speak again. Both " parting " (Theilung) and " budding" 

 (Knospenbildung) occur, then, in the Naids ; and it may be added 

 that the former appears to be peculiar to the genus Stylaria, or 

 to the proboscis-bearing forms. 



I may here remark that the distinction made by Schultze and 

 others between "Theilung" and "Knospenbildung," though con- 

 venient, does not seem to me a fundamental one. The mere 

 inclusion of a portion of parental tissue in the bud does not of 

 itself make an essential distinction between this and a wholly 

 new-formed, but otherwise similar, bud; nor have I been able 

 to see any histological or functional differences. The very fact 

 that individuals having the same genetic relations to the parent 

 stock are in one Naid (N. rivulosa) always or commonly pro- 

 duced by the so-called " budding," and in another genus (Sty- 

 laria) by the so-called " parting," leads to this view. Nor, as I 

 think, though observations are largely wanting in that direction, 

 have the two yet been shown to be functionally different in true 

 metagenetic processes. They are two varieties of one process ; 

 and it would be interesting in many ways to know exactly how 

 the various species of Naids already known follow distinctly the 

 one or the other plan, or tend to merge them yet more com- 

 pletely as one*. 



A little detail will show how closely identical the two forms of 

 bud-formation are. In " parting " (" Theilung "), as has already 

 to a great extent been described by Schultze, we find that, from 

 the parental ring as a fixed point, there is a continuous ring- 

 formation and elongation backward ; and that anteriorly to it 

 there is a limited elongation of the general body, also by ring- 

 formation from before backwards. There is, then, unlimited 

 growth backward from the fixed point, and a limited or defined 

 growth backward toward the fixed point from the place of fission. 

 The parental included ring, the most anterior of the series, is 

 here the fixed point. In " budding " (" Knospenbildung "), the 

 most anterior ring of the series also, though a wholly new-formed 

 one, becomes the fixed point, from which, by continuous ring- 

 formation, the Naid elongates backward, and towards which a 



* I have known " budding " to intercalate once in a series of fissions in 

 Stylaria longiseta (May 31), and I have also known " parting " to interrupt 

 a series of buddings in Nais rivulosa (Sjpt. 25), which leads me to expect 

 that in some Naids both processes may be regularly present. 



